Dry gloss pre-cast clay laminated paper and method of making it



DRY GLOSS PRE-CAST CLAY LAMINATED PAPER AND METHOD OF MAKING IT Frank D.Bergstein, Wyoming, Ohio, assignor to Bergstein Packaging Trust, a trustcomposed of Robert M. Bergstein and Frank D. Bergstein, trustees NoDrawing. Application February 7, 1957 Serial No. 638,680

22 Claims. (Cl; 154-97.5)

This invention relates to mineral coated paper or paperboard and to anew method for applying a surface layer of mineral coating material soas to develop any dseired surface finish inclusive of a high gloss orcast surface.

Heretofore, the application of mineral coatings to paper or board hasbeen performed in two ways:

1) The coating material is applied to the paper or board in the form ofa slurry, as by means of coating rolls, doctors or the like, whereuponthe coated paper or board is passed through calender rolls or the like.The resultant product is characterized in that it has a mottled orrelatively low finish.

(2) The paper or board is first coated with the mineral coatingmaterial, whereupon the coated surface is pressed against a polishedsurface, such as a chromium plated drum, and the coating dried while incontact with the drum. The resultant product has a surface finishcorresponding to that of the drum and is known in the art as a castsurface, being characterized in that it has a high gloss finish asoppsoed to the more or less mottled appearance of calendered stock.

The instant invention relates to a radical departure from the basiccoating methods characterized above and incorporates a wholly newconcept in the mode of application of a mineral coating to paper orpaperboard. Basically, the instant invention contemplates the precastingof the mineral coating layer on a surface other than the paper or boardweb followed by the application of the pre-cast or pre-formed layer assuch to the paper or board. This procedure results in numerousadvantages and effects savings which have hitherto never been obtainedin the field of mineral coated papers. This is particularly true asapplied to the high gloss or cast surface types of coated paper andboard.

In order to appreciate the problems solved by the instant invention, itmay be pointed out that the usual mineral coating layer cannot existapart from the surface on which it is formed. That is, conventionalmineral coatings do not have sufficient internal binding strength orbonding power to form a self-sustaining web or sheet which can behandled as such. The conventional mineral coating composition comprisesat least 70% finely divided mineral matter such as mineral clay orcalcium carbonate and not more than 30% binding agent such as casein,starch or alpha protein in aqueous suspension, with minor additions ofcoloring matter and other minor ingredients. A thin layer or coating ofsuch composition is frangible and will literally fall apart or powderwhen freed from the surface which supports it; and consequently, it hasbeen heretofore generally regarded that a mineral coating by its verynature could not be transferred or removed from the surface upon whichit is formed. Contrary to this accepted belief, I have found that underproper controls a conventional mineral coating can be (A atentransferred from one surface to the other without in any way disruptingthe integrity of the coating andwithout destroying or detracting fromany given surface characteristics, such as high gloss or the like, whichhas been imparted to the coating. In addition, I have found thatpre-cast coatings formed in accordance with my invention effectsubstantial savings in the amount of coatnig material required and inaddition overcome certain inherent disadvantages in mineral coatingprocedures as they are now practiced.

In accordance with my new process, a thin layer or coating of themineral coating composition is initially formed on a rigid surface, suchas a steel drum or belt, to Which the desired surface characteristicshave been imparted. The coating is rapidly dried in contact with thesupporting surface, whereupon the coating, now a lamina, is brought intocontact with the paper or board sheet to which it is to be transferred.This may be conveniently done by means of a roller positioned to bringthe sheet into contact with the coated surface of the drum or belt. Thecontacting surface of the sheet carries a coating of stripping orbonding adhesive which adheres to the mineral coating layer or laminaand, as the sheet passes around the relatively small circumference ofthe combining roll, a stripping action occurs causing the coating layeror lamina to be bodily transferred from the relatively non-adherentsupporting drum to the highly adherent adhesive surface of the sheet. Akey factor in the success of the transfer of the coating layer or laminafrom one surface to the other lies in the control of the moisturecontent of the combining adhesive so that insufiicient moisture orsolvent is present in the adhesive to strike through the mineral coatinglayer or lamina and disrupt its surface characteristics. Actually, twocontrols are involved. One is the degree of drying to which the coatinglayer or lamina is subjected and the other is the amount of moisture orsolvent in the adhesive. A balance can be effected between these twocontrols such that the coating layer or lamina may be simultaneouslyremoved from the surface against which it was formed and transferred tothe sheet to be coated or laminated.

A comparison of the present day method of forming a high gloss or castfinish with my new process will serve to illustrate the inherentdifferences between the two procedures.

(1) In the conventional high gloss coating operation the coating isperformed on a separate machine and requires special handling of thepaper or board roll. Due to the relatively slow speed of the coating anddrying steps, the process cannot be conducted as an incident of thepaper making operation and consequently the paper must be formed anddried on the paper making machine and wound into rolls which are thentransported to the coating machine where the rolls must be unwound,coated and the coated webs redried and re-rolled. As opposed to this, myprocess permits on the machine" application of the pre-cast mineralcoating immediately in advance of the winding station of a conventionalpaper making machine. Even as compared to the on the machine coating toprovide a low finish board, my process does not require the use ofmultiple coating boxes and additional drier sections which arecharacteristic of a machine coating operation.

(2) As already indicated, in a conventional cast coating operation themineral coating is applied directly to the paper or board web whereuponthe wet or plastic coated surface is brought into contact with a heateddrum and the sheet maintained in contact with the drum until the coatinghas become substantially dry or at least set to the extent that it issubstantially nonplastic. Inorder to secure adequate drying of thecoating, the coated sheet must be maintained in contact withthe drumfora substan;

3 tial length of time and the moisture in the coating driven off throughthe back of the sheet. In order to do this, the drum must be ofexcessively large diameter and its speed of rotation relatively slow ascompared, for example, to the lineal speed of a sheet running through apaper making machine. In addition, the conventional cast coatingoperation presents other problems due to shrinking and stretching of thepaper while in contact with the drum.

As opposed to this, in accordance with my process the coatingcomposition, which may be of conventional formulation is applieddirectly to a drum or other solid support having the desired surfacecharacteristics, and a layer of coating composition formed and dried insitu on such surface. The drying of the coating can be efiected in amatter of seconds since the moisture is driven off directly through theporous layer and does not have to be driven through the paper or boardsheet. In addition, the drying time is speeded up since both sides ofthe coating may be dried, the inner surface being dried by the heateddrum or the like and the outer or back surface by hot air, infra redlamps or other external heat applying means. The rapid drying of themineral coating to at least non-plastic condition enables me to pro-castand dry the mineral coating at a rate comparable to the speed of a paperor board making machine and hence apply the coating in an on the machineoperation.

(3) The driving off of the moisture through the board in theconventional drum coating operation roughens the back surface of thesheet, whereas in my process the subsequent transferral of the coatinglayer to the sheet in no Way alters the characteristics of the sheet assuch.

(4) With my process the sheet need not be permeable to water vapor ormoisture and hence the coating can be applied to any type of sheet nomatter how impervious it may be. Thus the sheet could be any type ofpaper, board, film, foil-backed board or the so-called KB board in whicha layer of bituminous material is interposed between the board surfaces.

(5) One of the major problems in casting a coated sheet against a drumlies in the necessity of maintaining all-over tight contact between thecoated sheet and the drum. Variations in the caliper of the sheet willresult in high or low spots in the coating which, unless perfectly tightcontact is maintained, will result in irregularities in the surfacefinish. In addition, the irregularities in the thickness of the coatingtend to result in non-uniform ink absorbency over the coated sheet. Withmy process the coating is applied directly to the drum or other supportand hence can be made uniform throughout. Any variations in the caliperof the sheet itself will be compensated for by the adhesive bondinglayer. The result is an excellent printing condition due to theuniformity of the coating with the resultant uniform ink absorbency overthe entire sheet.

(6) My coating procedure permits substantial economy in the amount ofcoating composition required in that none of the coating materialstrikes into the sheet as in the conventional coating operation. Themineral coating is laid in its entirety on top of the sheet with theresult that the amount of coating material required is substantially cutin half.

(7) While my procedure requires the use of an adhesive to bond thecoating layer to the sheet, inexpensive water borne adhesive may beemployed which does not add materially to the cost of the finishedproduct. Of course, if desired for specific application, other moreexpensive types of adhsive may be employed but such are not generallyrequired. Similarly, my process contemplates the use of conventionalmineral coating compositions without special additives, although hereagain such additives may be employed where special effects are desiredinclusive of the use of solvents or the like which might damage thepaper stock if applied directly to the stock and driven out through it,as in the conventional high gloss coating operation. With my'procedure,such solvents will have been driven oft prior to the association of thecoating layer with the sheet and hence there can be no deleteriousresults.

(8) Paper or board produced in accordance with my procedure will havesuperior flexibility and bendability as compared to conventional claycoated paper or board. The bending or foldability of mineral coatedpaper and board is a decided problem due in part to the fact that theclay or other mineral employed is inherently discrete particles heldtogether by a small quantity of binder and as such does not readilybend. To achieve a satisfactory end result a relatively heavy coatingmust be employed. However, due to the fact that I employ anadhesivewhich has high natural bending properties--to bond the mineralcoating to the board, the inherent flexibility and bendability of thecoating on a weight basis is materially enhanced.

It is, therefore, a principal object of my invention to provide aprocess of applying mineral coating to board having the advantageshereinbefore enumerated.

In carrying out my process, a conventional coating composition is firstprepared. The coating formula consists basically of pigment and binder.The pigment may be clay, calcium carbonate, or titanium dioxide, orcombinations of such pigments. The binder portions of the coatingformula may be either casein, alpha protein, or an acrylic polymer suchas an acrylic polymer resin emulsion or combinations of such adhesives.The percentage of pigment will be from to 70% and the binder range willbe from 10% to 30%. In addition to the basic ingredients, minorproportions of other ingredients such as dispersing agents, defoamers,or pH modifiers may also be employed.

The general procedure is to disperse the pigment in Water therebyforming a slurry of from 50% to 65% solids. If casein or alpha proteinis used, these are first cut in amonia Water at about 15% to 25% solids.In the case of emulsions they are usually used in latex form assupplied. The binder solution or emulsion is then added to the clayslurry and sufficient water added to bring the overall solids content ofthe coating to between 45% and 65%.

The slurry so formed is coated directly on the surface of a revolvingdrum or other supporting surface against which the coating is to set. Ihave found that the coating may be applied either by spraying or bydoctoring it on employing a wire-round rod or an air knife. The mannerin which the coating is applied does not constitute a limitation on theinvention although care should be taken to form a coating layer which isuniform and even throughout. While the coating may be of any desiredthickness, I have found that a highly satisfactory coated board may beobtained employing a coating having a thickness of about 1 mil.

The coating is dried on the drum or other support. I have found that adrum temperature of from 180 to 200 P. will cause rapid drying of thecoating composition and will cause it to set to a non-plastic condition.The drying time may be accelerated by applying external heat to thecoating, as by means of heated air passing over the drum, such airbeing, heated from to 200 F. In lieu of. heated air, infra red lamps orother suitable heat generating means may be employed, such means beingpreferably held to a maximum temperature at the coated surface of 200 F.When dried in this manner, I have found that the coating may be dried toa condition in which it may be readily transferred in a matter of about5 seconds where the coating has a thickness of substantially 1 mil.Consequently, where the drum has a diameter of 12 feet, it may berotated at a' lineal speed of 250 feet per minute which is comparable tothe normal running speed of a paper board machine. The mineral coatingwhen dry and bonded to said paper should consist of from 10 to 25 poundsof solid perream -Thed'rum lineal speed may vary from very slow speed ofl or 2 feet per minute up to 350 feet per minute depending on thickness,heat, and type of mineral coating applied. The speed of drying will,therefore, vary from 30 seconds to 1 second or less.

As already indicated, the mineral coating so formed may be transferredto any desired surface inclusive but not limited to paper, paperboard,chipboard, internally proofed boards, foil laminated boards and theso-called non-fibrous films. The web or sheet will be fed from asuitably positioned roll stand into contact with the precast coatinglayer. A relatively small diameter roller juxtaposed to the coated drummay be used for this purpose, the roller serving to bring the sheet intocontact with the coating and thereafter remove the sheet at an angle soas to, in effect, strip the adhered coating from the drum. As the sheetis fed from the roll stand, a stripping or bonding adhesive will beapplied to the surface thereof which will be juxtaposed to the coatinglayer. The stripping or bonding adhesive may be applied in anyconventional manner and may comprise a starch or protein base, polyvinylacetate or polyvinyl alcohol in which the solids content of the adhesiveis from 20% to 50% depending on type. Starch adhesives which consist of35 parts dextrine (converted starch), 60 parts water and 5 partsglycerine have been found satisfactory. Excellent adherence has beenobtained with only 2-3 pounds (solids) per ream (24 x 36/500). Polyvinylacetate based adhesives containing, approximately 37% solids consistingof polyvinyl acetate, tackifying resins, and plasticizers have also beenused successfully. These too have been applied at a rate of 23 pounds(solids) per ream (24 x 36/ 500). Though 2-3 pounds seems to be mostsatisfactory, the discrete adhesive layer may consist of from 2 topounds per ream (24 x 36/500) of dry adhesive.

'Drying of the stripping or bonding adhesive should take placeimmediately after application and before com bining with the mineralcoating. In the case of paper or paperboard this drying will take placemostly by absorption into the sheet, but external means such as warm airmay have to be employed. This step is necessary so that the moisture inthe adhesive layer does not disrupt the surface of the mineral coating.The combining should take place just before the adhesive becomesnon-adhesive and at its maximum wettack.

It has also been proven practical to apply a hot melt stripping orbonding adhesive and reactivate it by means of heat-at the instant ofcombining. The hot melt can be either applied in its melted state, insolvent solution, or in a suspended-in-water form. If applied in asuspended-in-water state, which is preferred, it must be driedcompletely before reactivation although since heat is used for bothdrying and reactivation it can be accomplished almost simultaneously. Anexample of this suspension is a polyamide suspensoid. Another example isvinylidene chloride and a plasticizer. This adhesive imparts to saidpaper a high degree of moisture-vaporproofness. The hot-melt adhesivesmay contain a percentage of wax to aid in moistureproofness or powderedaluminum, TiO clay, or CaCO in suspension to increase opacity of saidadhesive film.

In transferring the coating layer from the drum or other support, it isessential that the layer be maintained in substantially dry ornon-plastic condition. That is, the coating must be substantially dry atthe time it is brought into contact with the adhesive layer and, as toits cast surface at least, it must remain dry. Consequently, theadhesive must be controlled both as to amount and as to water or solventcontent so that it will not re-wet the coatinglayer to the extentthatthe solvent will penetrate to the cast surface thereof.- If the castsurface is re-wet by the adhesive solvent, it will not part from thedrum and,

even if the re-wetting occurs subsequent to the transfer .of the coatinglayer, the cast surface of the coating will be, impaired. To avoid thesedifliculties, themoisture or solvent content of the adhesive must be socontrolled that it is insulficient to penetrate the coating layer. Thiscontrol may be effected by (l) controlling the amount of water orsolvent present in the adhesive and (2) correlating the amount of wateror moisture present to the amount of residual heat in the coating layerat the time of transfer. Thus, a higher percentage of water or solventmay be present where the heat of the layer approaches 200 than where thelayer is heated to 160". In any event, the controlling factor lies inthe maintenance of the cast surface of the coating layer insubstantially dry condition during and subsequent to the transfer.

In accordance with my invention, the adhesive coating may serve a secondfunction in addition to its primary function as a bonding medium. Thus,the color and brightness of the finished product may be enhanced by theaddition of coloring agents to the bonding adhesive. Thus, satin white,blanc fixe and the like may be added to the adhesive which, in effect,provides a base for the coating layer which, as already indicated, mayalso contain dyes or other coloring agents. This is particularlyadvantageous where chipboard or other low grade stock is being coatedwhich does not have the brightness and uniformity in appearance of someof the more high grade types of board.

The following examples are representative of coating mixtures which maybe employed in accordance with my invention, it being understood thatthese formulations are exemplary only and do not constitute a limitationof my invention:

Ingredients Alpha Protein Acrylic Polymer Similarly, examples ofstripping or bonding adhesive compositions which may be used to bond thecoating layersuto the stock are as follows:

Stripping 0r bonding adhesives No. 1:

35 parts dextrine (converted starch) 60 parts water 5 parts glycerineNo. 2: plasticized polyvinyl acetate emulsion No. 3:

20 parts casein parts water 8 parts ammonia water It will be understood,however, that the coating method disclosed herein .is not limited to theuse of coating compositions containing Water nor is it limited to theuse of adhesive compositions containing Water. Either or bothcompositions may contain non-aqueous solvents or suspending agents whichmay be evaporated off either as an incident of the drying of the coatingor subsequent 'to the bonding of the coating layer to thesheet. However,it is competent to point out that my invention is particularly adaptedto use with water borne mineral coatings and water vehicle adhesiveswhich, for the most part, are less expensive and'more commonlyavailable.

Having thus described my invention, what I claim is:

1. A process for producing a paperboard sheet having a cast minerallayer adhesively bonded to one surface thereof, which comprises forminga thin coating of aqueous mineral coating composition on a castingsurface and drying it thereon, said coating composition consist- 'ingessentially of mineral pigment containing a minor proportion of binderwhich when dried forms a frangible and porous mineral layer, feedingtoward said mineral layer a web of paper-board and, as said paperboardis advanced, applying toone surface thereof a continuous coating of anadhesive material capable of adhering said paperboard to said minerallayer to form a bondtherebetween which is stronger than the bond betweensaid r'ninera'l layer and the said casting surface, bringing theadhesive coated surface of said paperboard into contact with saidmineral coating layer under sufficient pressure to" form an intimatebond therebetween, including the step of controlling the consistency ofthe bonding adhesive so that, upon contact with said mineral layer, saidadhesive will be non-saturating with respect thereto, and thereafterstripping said mineral layer from said casting surface by strippingforces applied to the paperboard, whereby to transfer said mineral layerintact from said casting surface to said paperboard to provide a castmineral layer intimately bonded to the surface of said paperboard.

2. A method of producing. a clay surfaced paperboard characterized. by acast clay finish, which comprises the steps of applying a thin,substantially uniform layer of mineral coating compcsition direct'y to acasting sur face and drying it thereon in the absence of externalsupport for said mineral layer, said mineral layer consistingessentially of an aqueous dispersion of mineral pigment containing aminor proportion of binder which when dried on said casting surface, isessentially frangible and incapable of self-support, feeding intocontact with said dried mineral layer a web of paperboard the contactingsurface of which is coated with a continuous film of bonding adhesive,controlling the consistency of said bonding adhesive so that, uponcontact with said mineral layer, said adhesive will be tacky and capableof intimately bonding to said mineral layer and yet incapable ofsaturating said mineral layer so as to wet the cast surface thereof, andthereafter utilizing said paperboard web to strip said mineral layerfrom said casting surface as a continuous discrete mineral coating layerthe exposed surface of which has a cast finish corresponding to thefinish of said casting surface.

3. A method of producing paper and paperboard having a cast mineralsurface, which comprises the steps of applying a thin, substantiallyuniform layer of mineral coating composition directly on a continuouslymoving casting surface, said mineral composition comprising a waterborne slurry composed essentially of a major proportion of mineralpigment and a minor proportion of binder, drying said mineral layer incontact with said casting surface with the surface of said mineral layeraway from said casting surface exposed so as to rapidly removesubstantially all of the moisture therefrom, thereby providing asubstantially dry frangible mineral layer, advancing a web of paper forcontact with the said mineral layer, and, as said paper web is advanced,applying to one surface thereof a continuous film of bonding adhesive,bringing the adhesive surface of said web into pressure contact with thedry mineral layer so as to effect an intimate. bond therebetween, thesaid bonding adhesive, at the time of its contact with said minerallayer, being sufiiciently free from moisture and other solvents capableof striking through the. mineral layer to its cast surface, so that saidcast surface will remain essentially dry, and thereafter stripping saidmineral layer from said casting surface by means of said web, saidmineral layer being firmly bonded to said web by said bonding adhesiveto provide an uninterrupted mineral coating supported on the surface ofsaid web and having its exposed face displaying the cast finish impartedto it by the said casting surface.

4. A. method of producing paper and paperboard having a smooth, highgloss, cast clay surface, which com prises providing a continuouslymoving, polished, endless casting surface,- continuously depositing onsaid casting surface a thin, substantially uniform layer of mineral.coating material consisting primarily of mineral pigment containing aminor amount ofv binder, drying said mineral layer in contact with saidcasting surface with the outer surface of said layer exposed, therebyforming afrangible mineral layer supported by said casting; surface,feeding a web of paper toward said casting surface and the dried minerallayer thereon, said web having on one surface thereof a continuous filmof bonding adhesive, bringing the adhesive coated surface of said'webinto contact with the dry mineral layer and' effecting. an intimate bondtherebetween, and thereafter stripping said web and the frangiblemineral layer b. .-'nded' thereto.- from said casting surface, wherebysaid mineral layer istransferred' intactto said web to provide a castcl'ay surface: thereon, including the step of main.- tainingthe saidmineral layer in substantially dry condition during its transfer to saidweb by controlling the saturating properties of the bonding adhesive.

5. A. method of producing paper and paperboard having a smooth, glossy,cast clay finish, which comprises providing a revolving cylindrical drumhaving a smooth, polished, casting surface, continuously depositing onsaid casting surface a thin, substantially uniform layer of wetmineralcoating. material consisting essentially of a water borne dispersion ofmineral pigment containing a minor amount of binder and drying saidlayer in contact with said. drum with the outer surface of said layerexposed, including the step of smoothing the said outer exposed surfaceof mineral coating material while still wet, whereby to form. afrangible mineral layer having a smooth exposed surface feeding a web ofpaper toward said drum and the dried mineral layer thereon, said webhaving on one surface thereof a continuous film of bonding adhesive,bringing the adhesive coated surface of said web into pressure contactwith the dry layer at a time when the adhesive coating is sufiicientlytacky to firmly bond to the mineral layer and yet contains insufficientmoisture and other solvents to penetrate the mineral layer so as to wetthe cast surface thereof, and thereafter stripping the mineral layerfrom said drum by leading the web away from said drum, said minerallayer being thereby removed intact from said drum to provide a castlayer of uniform thickness supported entirely on the surface of said weband. intimately bonded thereto.

6. The method claimed in claim 2 wherein said mineral layer comprisesfrom 70% to of a pigment selected from the group consisting of clay,titanium dioxide and calcium carbonate, and from 10% to 30% binderselected from the group consisting of alpha protein, casein, and acrylicpolymer. I

7. Themethod claimed in claim 2 wherein said mineral layer is driedagainst said casting surface by heat applied 1in part, at least, to theexposed outer surface of said ayer.

8. The method claimed in claim 2 wherein said bonding adhesive issubjected to heat immediately prior to the bonding together of said weband said mineral layer.

9. The method claimed in claim 2 wherein said bonding adhesive is awater-borne adhesive applied to said web as it is advanced toward saidcasting surface, and wherein said adhesive, prior to contact with saidmineral layer, is subjected to heat in a quantity sufficient to retainits tack and yet reduce its moisture content to a point wherein itsconsistency is non-saturating with respect to said mineral layer.

10. The method claimed in claim 2 wherein said bonding adhesive is a hotmelt adhesive applied in a melted state.

11. As an article of manufacture, a paperboard sheet having intimatelybonded to one surface thereof a thin,

continuous layer of essentially mineral matter having a cast surface,said mineral layer being of substantially uniform thickness throughoutand bonded to said paperboard. sheet by a continuous, thin filnr ofbonding ad;

hesive, said mineral layer being characterized by being a pre-formedfrangible layer dried on a supporting casting surface and, upon beingthereafter adhesively bonded to said paperboard sheet, defining adiscrete mineral coating layer supported in its entirety on the surfaceof said paperboard sheet.

12. As an article of manufacture, a sheet of paper stock havinglaminated to one surface thereof a thin, continuous, discrete andnormally frangible layer of essentially mineral pigment having apre-formed cast surface, said mineral layer being intimately bonded tothe surface of said web by a continuous film of bonding adhesiveinterposed therebetween, said bonding adhesive serving to firmly anchorsaid otherwise frangible mineral layer to the surface of said webwithout disturbing the pre-formed cast surface of said mineral layer.

13. As an article of manufacture, a Web of paperboard having adhesivelybonded to one surface thereof a smooth, continuous and substantiallyuniform layer of essentially mineral composition having a cast surface,said mineral layerbeing characterized by having been deposited on anddried against a casting surface and having a smoothed surface oppositethe cast surface thereof, and thereafter intimately bonded to said webby an interposed film of bonding adhesive, said mineral layer beingfurther characterized by being normally frangible and having been bodilyremoved from the casting surface upon the application to said web ofstripping forces sufiicient to strip said mineral layer from the castingsurface on which it was formed.

14. A porous clay coated paper suitable for printing in which the claycoating has a cast surface formed by drying the coating against acasting drum, said cast coating being characterized by having beenpreformed apart from its paper backing from an aqueous dispersion ofmineral pigment containing a minor proportion of binder and, when dried,bonded to said backing by a continuous film of bonding adhesive, saidcast coating being further characterized by a smoothed and even backsurface which results in a coating of substantially uniform thicknessthroughout, thereby providing substantially uniform printing inkreceptivity.

15. The clay coated paper claimed in claim 14 wherein said bondingadhesive contains a coloring agent.

16. The clay coated paper claimed in claim 14 wherein said bondingadhesive is of a moisture-vapor proofing character.

17. A process for the manufacture of mineral coated paperboard having acast finish which comprises forming on a traveling casting support athin substantially uniform layer of an aqueous mineral-adhesivecomposition having a solid content consisting essentially of mineralpigment and binder in a ratio of 70-90 parts pigment to 3010 binder,drying said layer to render it, substantially free of liquid vehicle andcharacterized by porosity at least suificient to accept printing inks,forming on a paperboard web a coating of adhesive material and temperingsaid coating to a substantially solvent free nonsaturating consistencywhich nevertheless is characterized by surface tack, bringing the coatedsurface of said paperboard web against the coating on said castingsurface, applying suflicient pressure to cause said adhesive to bondwith said dried mineral-adhesive coating, and concurrently strippingsaid paperboard web and both coatings from said casting surface.

18. A process for making paperboard having a cast coating thereoninvolving the separate formation of a frangible and porous mineralcoating layer in final dried form on a moving casting support and theremoval of said frangible dried coating from said support onto thesurface of a paperboard web in finished substantially dry form,therebeing interposed between said web and said coating a layer ofadhesive substance having an affinity for the mineral coating but havinga non-saturating consistency with respect thereto, in which process thepaperboard layer bearing a coating of said adhesive in the formspecified is laid against the dry coating on said support and in whichadherence between the said adhesive layer and the said mineral coatingis brought about primarily by the application of pressure prior to thestripping of the said board and both coatings concurrently from the saidcasting support.

19. A process of forming a cast coated paperboard printing stock whichcomprises producing upon a moving casting support a substantiallyuniform and porous layer of mineral coating composition which isfrangible in dried condition, and thereafter transferring the saidfrangible mineral layer to the surface of a paperboard Web and adheringit thereto by a non-saturating adhesive, said adhesive acting to bondsaid paperboard web to said mineral layer While the latter is in contactwith said casting support, whereupon said mineral layer may be strippedintact from said casting support by pressure applied to said paperboardweb.

20. The process claimed in claim 19 wherein said non-saturating adhesiveis of moisture proofing character, whereby .to establish a moistureproofing barrier immediately beneath said porous layer of mineralcoating composition.

21. A method of making clay coated paper and board which comprisesapplying an aqueous mineral coating composition to a casting surface,the solids constituent of said composition consisting essentially ofmineral pigment and a minor proportion of binder, smoothing and dryingsaid mineral coating on said casting surface, thereby forming anessentially frangible coating supported by said casting surface, saidcoating being characterized by a smoothed surface opposite the castsurface thereof, and thereafter transferring said dried mineral coatingintact onto the adhesive-coated surface of a web of paper or board.

22. A method making coated paper and board which comprises continuouslyapplying a water borne slurry of mineral coating composition to a movingcasting surface, said slurry containing solids consisting essentially ofmineral pigment and binder in a ratio of 70-90 parts pigment to 30-10parts binder, drying said slurry on said surface so that the driedmineral layer so formed acquires the surface characteristics of thecasting surface, separately applying a film of adhesive to a movingpaper web, bringing said adhesive film to a state wherein it is tackyyet non-saturating with respect to said dried mineral layer, andthereafter continuously pressing the adhesive film into contact withsaid dried mineral layer under suflicient pressure to effect a bondtherebetween, and thereafter continuously stripping said mineral layerfrom said casting surface by means of said web, whereby to transfer saidmineral layer to said web while retaining the cast surface impartedthereto by said casting surface.

References Cited in the file of this patent UNITED STATES PATENTS1,930,331 Zimmer Oct. 10, 1933 2,158,987 Maloney May 16, 1939 2,236,766Schneider Apr. 1, 1941 2,286,259 Cagle June 16, 1942 2,295,814 WagerleSept. 15, 1942 2,487,448 Kingerley Nov 8, 1949 2,641,557 Green June 9,1953 2,704,735 Hedges et a1 Mar. 22, 1955 2,733,180 Pinto Jan. 31, 19562,739,919 Artzt Mar. 27, 1956 2,771,388 Rocky Nov. 20, 1956 2,796,374Donahue June 18, 1957 2,801,949 Bateman Aug. 6, 1957 2,813,052 LancasterNov. 12, 1957 2,819,196 Munro Jan. 7, 1958 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent Nob 2 .934,467 April 26., 1960 Frank D,Bergstein It is herebjr certified that error appears in theprintedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column l line 18, for "dseired" read desired line 35 for "-oppsoed" readopposed column 2, lines 5 and 6 for "coatnig" read coating column 7,line 28-, after "which" insert a comma; column 8, line 3O for "'surfaceread surface line 32 after "surface" insert a comma; column 9, line 54after "30-10" insert parts same line 54L after "it" strike out thecomma; same column 9, line 7'3 for "'thereloeing-" read there beingSigned and sealed this 4th day of April 1961.,

(SEAL) Angst; a RNEST W. SWIDER ARTHUR W. CROCKER Attcsting Ofii erActing Commissioner of Patents

3. A METHOD OF PRODUCING PAPER AND PAPERBOARD HAVING A CAST MINERALSURFACE, WHICH COMPRISES THE STEPS OF APPLYING A THIN, SUBSTANTIALLYUNIFORM LAYER OF MINERAL COATING COMPOSITION DIRECTLY ON A CONTINUOUSLYMOVING CASTING SURFACE, SAID MINERAL COMPOSITION COMPRISING A WATERBORNE SLURRY COMPOSED ESSENTIALLY OF A MAJOR PROPORTION OF MINERALPIGMENT AND A MINOR PROPORTION OF BINDER, DRYING SAID MINERAL LAYER INCONTACT WITH SAID CASTING SURFACE WITH THE SURFACE OF SAID MINERAL LAYERAWAY FROM SAID CASTING SURFACE EXPOSED SO AS TO RAPIDLY REMOVESUBSTANTIALLY ALL OF THE MOISTURE THEREFROM, THEREBY PROVIDING ASUBSTANTIALLY DRY FRANGIBLE MINERAL LAYER, ADVANCING A WEB OF PAPER FORCONTACT WITH THE SAID MINERAL LAYER, AND, AS SAID PAPER WEB IS ADVANCED,APPLYING TO ONE SURFACE THEREOF A CONTINUOUS FILM OF BONDING ADHESIVE,BRINGING THE ADHESIVE SURFACE OF SAID WEB INTO PRESSURE CONTACT WITH THEDRY MINERAL LAYER SO AS TO EFFECT AN INTIMATE BOND THEREBETWEEN, THESAID BONDIND ADHESIVE, AT THE TIME OF ITS CONTACT WITH SAID MINERALLAYER, BEING SUFFICIENTLY FREE FROM MOISTURE AND OTHER SOLVENTS CAPABLEOF STRIKING THROUGH THE MINERAL LAYER TO ITS CAST SURFACE, SO THAT SAIDCAST SURFACE WILL REMAIN ESSENTIALLY DRY, AND THEREAFTER STRIPPING SAIDMINERAL LAYER FROM SAID CASTING SURFACE BY MEANS OF SAID WEB, SAIDMINERAL LAYER BEING FIRMLY BONDED TO SAID WEB BY SAID BONDING ADHESIVETO PROVIDE AN UNINTERRUPTED MINERAL COATING SUPPORTED ON THE SURFACE OFSAID WEB AND HAVING ITS EXPOSED FACE DISPLAYING THE CAST FINISH IMPARTEDTO IT BY THE SAID CASTING SURFACE.